Army, a large body of men (and sometimes women) trained and armed for land warfare. An army mainly comprises of ground troops, their weapons and equipment, and military bases. Infantry, armored vehicles, and artillery along with additional support troops who handle transportation, medical care, and other responsibilities are also part of the army.

The size and strength of armies varies greatly as it is dependent on many factors. A countrys economy plays a major role as wealthy nations are able to expensive weapons and pay large numbers of soldiers.

Today, all developed nations maintain armies with large numbers of tanks, armored personnel carriers, helicopters, and even ships. The less developed nations that cannot afford to have advanced weapons often have to depend on specially trained light infantry, small ground attack aircraft, and armored cars.

Switzerland, does not maintain a standing army of professional soldiers as it has very less potential enemies. Instead it has opted for a large national militia of men who can be called into service during crisis situation. France, the United Kingdom, and the United States have extensive foreign commitments and hence, require a huge standing army to meet their international needs.

There are differences in the way countries raise and maintain their army. While some use a military draft, others have universal military service, which necessitates that all qualified men and women in a certain age range serve. There are also some nations that have an entirely volunteer army. In present times, women are included in almost all armies.

Armies are divided into regular army and an army reserve by most of the nations. The professional soldiers constitute the regular army and receive regular training and are always on active duty and ready for combat. It is not affordable for nations to maintain a regular army large enough to meet any crisis. A large amount of army reserve is even maintained by those nations that mostly rely on regular forces. This reserve is also called a national guard or militia and trains citizens for immediate active duty in an emergency.

The biggest units of some armies are called army groups, comprising several hundred thousand soldiers. 50,000 to 100,000 soldiers form a single corps, and many such corps forms an army. Each of the corps is divided into two or more divisions and any necessary support troops.

The basic fighting unit of many armies is known as the division, which include infantry, armored forces, and artillery; and engineers, who are also sometimes considered as combat troops. Support troops who handle transportation, medical care, and other responsibilities are also included in the divisions. Divisions usually are identified according to their equipment, training, and function. Infantry, mechanized, armored, and airborne divisions are included in the types of divisions. Each of the division may vary in size from about 10,000 to 18,000 soldiers. In addition most of the divisions have three or more brigades of roughly equal size, and each brigade has three to five battalions. The battalion, which is a combat unit of 500 to 800 soldiers, is further divided into groups of 100 to 200 soldiers. Infantry and armored units of this size are generally known as companies. Artillery groups also known to be as batteries and groups of cavalry are called troops.

Armies are mainly used by the nations to conquer enemy territory and also to defend itself from attack. Army plays a role in preventing war during peacetime and also come to the rescue of civilians in certain emergencies. As an example of armies preventing war was in 1991, when French and Belgian troops went to Zaire, now Congo (Kinshasa), to restore order after Zairian soldiers rioted.

Tactical nuclear weapons were developed in the mid 20th century, which gave armies an important defensive strategy. These weapons were designed with the purpose of being used in places where a conventional war was being fought. The army, which massed its men and equipment, was vulnerable to a nuclear attack. The fear of being faced with such an attack could prevent a nation from attacking an enemy. This idea is called deterrence and was used by the Soviet Union and Western nations from the end of World War II in 1945 to the late 20th century, which was a period of hostility known as the Cold War.

The term army refers both to the complete ground forces of a country and also to a large tactical unit (more properly called a field army), such as the U.S. Fifth Army. In this article, the more general meaning is intended—"army" means all of a nation's ground forces. An army's ranking is based on its overall fighting strength, which in turn depends on the number of troops on active duty, well-trained soldiers and modern weapons. A small army with tactical nuclear weapons may possess greater attacking power than a huge army with antiquated weapons.

Nations like China, India, North Korea, Russia, the United States, France, and the United Kingdom have the worlds major armies. Excluding India and North Korea, all other nations armies have tactical nuclear weapons. But, India and North Korea have the potential to produce such weapons in future.

China's army, with a force of approximately 2,900,000, is the world's largest. The country has nearly 1 1/2 million troops on active duty. A large number of the Chinese forces are assigned to defensive positions near the Russian border in northeastern China. About 800,000 of the Chinese army have people in its reserve and armed militia. China uses a military draft.

The U.S. Army, excluding personnel not on active duty, has a strength of about 509,000. The United States Army has about 500,000 troops on active duty. Armies are stationed in the United States, Western Europe, Japan, South Korea, and parts of Latin America and the Middle East. The United States Army mainly comprise of volunteers. The largest European armies are those of Russia and Germany. Russia has an army of approximately 460,000; Germany's is estimated at 255,000. The Russian Army, which is officially called the Ground Forces of the Russian Federation, has about 400,000 troops on active duty. A large number of Russian armies are posted along Russia's border with China. Following the breakup of the Soviet Union in 1991, Russia began to organize its army in 1992. The Russian army has small forces in the former Soviet republics of Georgia, Moldova, and Tajikistan. The army has both volunteers and draftees. Russian soldiers can serve in the reserve until the age of 50 after 18 months of active duty.

There are about 1,100,000 men on active duty, about 300,000 in the reserve, and about 40,000 in the Territorial Army of the Indian Army. Mainly as doctors and nurses, only a few hundred women serve in the Indian Army. All members of India's Army are volunteers.

There are about 950,000 troops on active duty and about 600,000 in the reserve of the North Korean Army. Men from the ages of 20 to 25 are drafted to serve for five to eight years. After their service is over, the men can serve part-time in local militias until the age of 40 and then in the Red Guard until the age of 60. Women may join the army on a volunteer basis.

The French Army comprise of about 135,000 members on active duty and 11,000 in the reserve. Countries like Western Europe, several African countries, and in France's overseas territories, French troops are mainly stationed. The French Army has both volunteers and draftees.

There are about 115,000 troops on active duty, about 200,000 people in the reserve, and about 40,000 members of the Territorial Army of the British Army. British troops are stationed in Germany, Northern Ireland, and many other parts of the world. All members of the British Army are volunteers.

Other countries like Egypt, Iran, Myanmar, Pakistan, South Korea, Turkey, and Vietnam also have a major army presence. All these countries have 300,000 or more troops on active duty. The armies of these countries have purchased weapons and equipment from the world's major powers. None of these nations has tactical nuclear weapons; however Pakistan has the potential to produce them.

From about the 16th century until the 20th, armies generally had three combat arms, or branches: infantry, the foot soldiers with rifles and bayonets; artillery, with the big guns; and cavalry, shock troops that fought on horses with lances, sabers, carbines, and pistols. The first two combat arms are still used, but cavalry has been replaced by armor, a powerful striking force equipped with tanks and other fighting vehicles. Modern warfare requires such close cooperation among these branches that the distinction between them is disappearing. In the early 17th century, the importance of navies increased equal to that of land forces. In the early 20th century, military aircraft first came on the scene, changing the face of warfare permanently. Today, many nations have started using their armies in combination with air and naval units in joint operations. Military alliances, which began to rise in the 18th century had led to the development of combined or coalition warfare, which involves the military forces of several nations.

Nuclear weapons, missiles, and many other new weapons cannot be fitted neatly into the traditional branches of service. Missiles fired from fixed mounts may be handled by artillerymen, but other missiles—some as large as artillery shells—may be fired from a simple tube handled by one infantry soldier. Infantrymen may march to battle as they have for hundreds of years, or they may be carried in armored cars or in helicopters, or parachuted from planes.

At various times throughout history, armies have been made up of professional soldiers, mercenaries, volunteers, or conscripts. Some nations have used two or more of these types at the same time.

A professional, or regular, army is made up of soldiers who devote their careers to the military service of their country. Nearly all nations support a standing army of this type, prepared to fight on a moment's notice. Mercenaries are soldiers who will fight for any country that pays them. Volunteers are men who enlist in time of war or national emergency. A conscript army consists of men drafted, or conscripted, by the government.

Not all members of an army take part in fighting. Combat troops require a variety of supporting troops—cooks to prepare food, truck drivers to haul supplies, mechanics to repair equipment. Every fighting soldier in the U. S. Army during World War II was supported by three or four men behind the lines.

Most large armies are organized into two or more field armies. Other units, listed in order of decreasing size, are corps, divisions, brigades or regiments, battalions, companies (or batteries), platoons, and squads. The size of each of these units varies from time to time and country to country.